Immunopathology of childhood idiopathic thrombocytopenic purpura.

Modern laboratory techniques have begun to elucidate the pathophysiology of chronic childhood ITP. Quantitative assays of PAIgG, complement, immune complexes, and platelet kinetic studies have all provided important information. Chronic ITP of childhood appears to be similar to adult ITP, with production of an antibody directed against platelets and megakaryocytes. Most of the antibody is produced in the spleen, but other parts of the RES can also produce antibody. Complement, immune complexes, and cell-mediated immunity may play a role in the pathogenesis. Sensitized platelets are cleared by the RES, particularly in the spleen. Platelet kinetic studies show that platelet turnover is usually rapid with compensatory increased thrombopoiesis, but there are some patients who have decreased thrombopoiesis. Acute ITP of childhood is a brief illness, characterized by abrupt onset of hemorrhagic symptoms and complete recovery. It often follows a viral illness, suggesting that immune complexes as well as antibodies are important in the pathogenesis. Both the spleen and liver may be important organs of immune clearance.